Very unusual '7747 .bin ~ 7.4 liter / 700R4

[EagleMark]

I can't use your BPW calculater on this desktop PC, no Open Office, my laptop is dead... But the Excel version comes out to 129.4 BPW.

Anything we are looking for in log?

[EagleMark]

If you choose Paremeter Catagory in the XDF go into Hacks and apply the Spark Advance and BPW hacks. You can then log spark advance and see BPW time and Injecter Duty cycle % when you get to WOT.

IAC counts are very high at idle, 80-90, turn the screw in half turn and re start. Watch them at full warm up and get down to 20ish, will idle much better letting air and fuel mix while still leaving room for IAC to control idle. TPS voltage will increase but not effect anything till 1.00 volt mark, can readjust TPS voltage later back to .54

[dave w]

If you choose Paremeter Catagory in the XDF go into Hacks and apply the Spark Advance and BPW hacks. You can then log spark advance and see BPW time and Injecter Duty cycle % when you get to WOT.

IAC counts are very high at idle, 80-90, turn the screw in half turn and re start. Watch them at full warm up and get down to 20ish, will idle much better letting air and fuel mix while still leaving room for IAC to control idle. TPS voltage will increase but not effect anything till 1.00 volt mark, can readjust TPS voltage later back to .54

I think there is a vacuum leak around the throttle blade shaft. I can't get the IAC counts down. Nothing special to look at in the logs. With some cells lean and some cells rich, I've decided to adjust the VE Table.

I'll work on getting the spark advance in the logs latter on.

I've tried BPW 136, too lean.

dave w

[EagleMark]

Vacuum leak will usually bring IAC count down...

Changing desired IDLE CL will also change IAC counts if you have raised idle.

Idea I use, keep BPW where it should be 129? Change Injector Bias from BB .274 to SB .396 or raise more... I have run to .500 without causing other issues...

HTH!

[Six_Shooter]

Vacuum leak will usually bring IAC count down...

This ^^^

Vacuum leaks usually cause high idle with low IAC counts, not the other way around.

[dave w]

IAC connector pic. Upper two pins have corrosion.

dave w

[dave w]

Vacuum leak will usually bring IAC count down...

Changing desired IDLE CL will also change IAC counts if you have raised idle.

Idea I use, keep BPW where it should be 129? Change Injector Bias from BB .274 to SB .396 or raise more... I have run to .500 without causing other issues...

HTH!

I'll try changing the injector bias. That is something I've not needed or tried to do before.

[EagleMark]

IAC connector pic. Upper two pins have corrosion.

dave w

There's also 2 wires swapped on BB IAC! never figured that out either why same ECM and parts but 2 wires swapped on BB. Your truck has also had an IAC plug change, that truck harness came with sqaure plug IAC.

All wiring diagrams floating around are SB and don't show the change. I had a pdf with the 2 swapped on my dead laptop, we'll see how much I got before the reformat...

[dave w]

There's also 2 wires swapped on BB IAC! never figured that out either why same ECM and parts but 2 wires swapped on BB. Your truck has also had an IAC plug change, that truck harness came with sqaure plug IAC.

All wiring diagrams floating around are SB and don't show the change. I had a pdf with the 2 swapped on my dead laptop, we'll see how much I got before the reformat...

Good thinking on the IAC wiring. I'll investigate the IAC wiring tomorrow. I'll use the '7747 wiring diagram for a 454 and use an ohm meter.

The attached .xdl is after changing the injector bias a small amount. I noticed the INT are better, but at the beginning of the data log it looked like all the BLM's were going to rich. Then at the end of the data log, the BLM's changed to near normal or slightly lean.

dave w

[EagleMark]

Good thinking on the IAC wiring. I'll investigate the IAC wiring tomorrow. I'll use the '7747 wiring diagram for a 454 and use an ohm meter.
dave w

Post up a diagram if you can.

The attached .xdl is after changing the injector bias a small amount. I noticed the INT are better, but at the beginning of the data log it looked like all the BLM's were going to rich. Then at the end of the data log, the BLM's changed to near normal or slightly lean.

dave w

No attach? Did you change BPW back to calculated value?

Rich at beginning and better at end, if it was warmed up the whole time I would say you didn't disconnect power to loose the BLM learn and it was correcting from what it had before the injector bias change? With engine warmed up and driven, kill power to ECM, start and when goes closed loop do quick data logs just a few minutes. Three runs at 20% TPS, 40% TPS and 60%TPS, adjust VE, smooth table rinse and repeat! Use the wire frame view to finish shaping/smoothing Main VE Fuel Table. Really sped up building a VE table for me.

Back to BPW calculated value. This is what has happened every time I test changing BPW from that value, weird things happen high and low from where you were. I did this on a stock truck/engine with a perfect tune. Increased BPW and bottom end got rich and top end went lean. Why? I don't know but it has happened every time every vehicle. Next time I think I'll try the opposite and decrease BPW to see if BLM goes opposite.

HTH!

[RobertISaar]

Increased BPW and bottom end got rich and top end went lean. Why? I don't know but it has happened every time every vehicle. Next time I think I'll try the opposite and decrease BPW to see if BLM goes opposite.

the answer to why is one that requires you to be familiar with the way GM calculated a BPW from the BPC based masks.

the short answer is that moving the BPC is one direction will cause the table values to spread out more than reality while moving it in the other direction will cause them to group closer together. let's say with a stock VE table and stock BPC value that you see 20% VE in the weakest part of the table and 80% at peak torque. based on what you've stated, moving the BPC upwards will cause the values to spread apart(now something like 15% and 85%). a small decrease should change them to 25% and 75%.

again, that's the short (and simple) answer, but it's accurate.

[PJG1173]

Post up a diagram if you can.

I found this on another site a couple of weeks ago while wiring my conversion up. it show's the two wires swapped for the BB TB.

[dave w]

the answer to why is one that requires you to be familiar with the way GM calculated a BPW from the BPC based masks.

the short answer is that moving the BPC is one direction will cause the table values to spread out more than reality while moving it in the other direction will cause them to group closer together. let's say with a stock VE table and stock BPC value that you see 20% VE in the weakest part of the table and 80% at peak torque. based on what you've stated, moving the BPC upwards will cause the values to spread apart(now something like 15% and 85%). a small decrease should change them to 25% and 75%.

again, that's the short (and simple) answer, but it's accurate.

Robert, I've never fully understood the BPC vs. VE workings. Thank you, your explanation helps!

dave w

[dave w]

I found this on another site a couple of weeks ago while wiring my conversion up. it show's the two wires swapped for the BB TB.

I have a used factory 7.4 liter '7747 wiring harness I used an ohm meter on. Using the orientation that the 454 IAC connector is plugged into the throttle body;

Top of IAC Connector
LT BLU / BLK C6
LT BLU / WHT C5
LT GRN / WHT C4
LT GRN / BLK C3

dave w

[EagleMark]

the answer to why is one that requires you to be familiar with the way GM calculated a BPW from the BPC based masks.

the short answer is that moving the BPC is one direction will cause the table values to spread out more than reality while moving it in the other direction will cause them to group closer together. let's say with a stock VE table and stock BPC value that you see 20% VE in the weakest part of the table and 80% at peak torque. based on what you've stated, moving the BPC upwards will cause the values to spread apart(now something like 15% and 85%). a small decrease should change them to 25% and 75%.

again, that's the short (and simple) answer, but it's accurate.

That would also explain why it is so important in this mask to keep BPW calculated properly and also explain why there is 2 VE fuel tables. Look at VE1 and it is very low resolution so with BPW not being correct the spread is to far.

This week I did another 7747 truck and from boredom used both VE tables. VE2 set to 30% and the tune went smoother then usual? Because I am so used to tuning this ECM? Or because I spread the low resolution load? Just thoughts but I think I'll use this method again. Although using the BLM spreadsheet is not as accurate in VE1 as it is not 100% of calculated fueling anymore.